David, I think it depends on the thickness of your quilt "sandwich". Why don't you make up a sample that is approximately the same thickness of your quilt and experiment on iwithout the foot and mastering the decorative stitch.. On thinner quilts I have quilted withour the walking foot, but the foot does help move all three layers better.
Don't try using the walking foot with the decorative stitch because the needle may hit the foot and break possibly causing you or your machine damage.